Funny things can happen on a new frontier. Take radio astronomy, for example. It really only kicked off in the 1950s, after Karl Jansky’s first detection of an astronomical radio source – the centre of our Milky Way Galaxy – in 1933, and after World War Two saw radio technology advance in leaps and bounds. In those early days on this new astrophysical frontier, radio astronomers were detecting new and bizarre phenomena aplenty, and it was taking some time for the physics to catch up so that we could explain these phenomena. Through a lack of experience, and a small but growing sample size, it was easy to sometimes jump to conclusions.
The first primitive radio surveys of the sky detected all kinds of weird and wonderful sources of radio waves. Some of them seemed exceptionally powerful, and to the crude sensitivity of the radio telescopes of the time, they seemed unchanging.
So when one of these powerful radio sources was observed to vary, it set imaginations running wild.
During the early 1960s, some of the leading radio astronomers in the world were in the Soviet Union, where radio astronomy was maturing fast, along with a keen interest in the search for extraterrestrial intelligence (SETI). Among those pioneering radio astronomers were Nikolai Kardashev and Gennady Sholomitskii. In 1963, Kardashev had proposed a three-tier system for classifying extraterrestrial civilisations depending upon their energy consumption, and he’d suggested that some of the brightest radio sources could be powerful beacons produced by civilisations at the higher end of his scale.
One of these sources was CTA-102, its name referring to the fact that it was the 102nd object discovered by radio astronomers for the ‘Caltech Catalog A’. Using the Crimea Deep Space Station, Sholomitskii observed CTA-102 for several months, seeking any sign that might be artificial. He soon had his wish, for lo and behold he began to observed slow changes in its radio brightness, as though someone had their hand on the volume button, turning the strength of the radio waves up and down.
This was a surprising turn of affairs. To Sholomitskii’s knowledge, during radio astronomy’s fledgling history, none of these powerful radio sources had ever been seen to vary in brightness over time. So he jumped to a conclusion: it had to be an artificial SETI beacon of the kind described by Kardashev. Sholomitskii was so excited that he had his home institution, the Sternberg Astronomical Institute in Moscow, call a press conference to announce his discovery. Journalists came from all across the Soviet Union to hear the news of the extraterrestrial civilisation that Sholomitskii had discovered billions of light years away. The news soon spread to other parts of the globe too, and astronomers in other countries were eager to hear more of the details. However, contrary to what Sholomitskii had though, it quickly it came to light that sources of variable strength were known to astronomers, and that the variability was being seen more and more in a class of objects called quasars, which are found in exceptional – and distant – galaxies.
Sholomitskii was embarrassed, but it was an important lesson that SETI had to learn. Furthermore, as one of the eminent radio astronomers of the time, Sholomitskii was no crank, and although he hadn’t found aliens, his observations of CTA-102 were vitally important in eventually figuring out the mechanics of quasars and other active galaxies: the radio emission comes from the vicinity of a powerful supermassive black hole in the centre of such a galaxy. The variability is just the result of changes in the amount of matter feeding the black hole.
This was SETI’s first major false alarm, but it would not be the last. Such instances are often used to ridicule SETI, but in truth, false alarms can be incredibly important, not only in fine-tuning our search for extraterrestrial life, but also as dry runs for the day we really do make contact.
Another false alarm that resulted in a major advance in astrophysics occurred in 1967, when Jocelyn Bell–Burnell discovered the first known pulsar. I describe this story of discovery in detail in my book The Contact Paradox, but Bell-Burnell’s supervisor Anthony Hewish and the head of their department, Martin Ryle, were far more circumspect in dealing with the matter than Sholomitskii had been. Although they did not discount the possibility that the pulsing signal that Bell–Burnell had found was artificial, they knew they had to rule out all other possibilities first. Hewish scrutinised the scientific literature to come up with a plausible mechanism – a spinning neutron star beaming radio jets from its magnetic poles. When they released their findings early the following year, there was a press scrum, just as their had been for Sholomitskii. However, this time the press were not treated to rash claims about ET, but rather one of the greatest astronomical discoveries of the twentieth century.
Not so secret
Admittedly, not all of SETI’s false alarms coincide with giant leaps in our astrophysical knowledge, but that doesn’t mean we can’t learn from them. In Seth Shostak’s book Confessions of an Alien Hunter, the SETI Institute astronomer describes how, in June 1997, the 42-metre dish at Green Bank radio observatory had detected an unusual signal coming from space. As Shostak and his fellow SETI astronomers monitored it over a 24-hour period, Shostak received a phone call from a journalist at the New York Times, asking if progress had been made on ascertaining the origin of the signal. Shostak was amazed that the journalist had found out about the signal, since nobody outside of the group of relevant astronomers had yet been alerted to its existence, as is standard procedure until they could confirm what the signal was. Nobody wanted to repeat the mistake of Sholomitskii.
As it turned out, they were correct in being cautious, because the signal wasn’t extraterrestrial at all. Instead, Shostak and his colleagues had unwittingly been tracking signals coming from the joint NASA and ESA Solar Heliospheric Observatory (SOHO) mission to observe the Sun. These false alarms happen all the time and are usually quickly figured out, but what the episode taught Shostak was that keeping news of a SETI detection secret would be nigh on impossible. People talk, and leaks happen. So much for conspiracy theories that suggest governments would keep such discoveries secret.
The realisation of the nature of quasars and pulsars happened relatively fast, in terms of the time elapsed since the first detection and figuring out what they were. Often it can take years, decades even, between discovery and denouement.
Fast bursts, slow science
Fast radio bursts, or FRBs for short, are a classic example. These incredibly brief bursts of radio waves went completely unnoticed, until the first to be discovered was found by chance. In 2007, astronomer Duncan Lorimer and his colleagues had been analysing archive data from the Parkes radio telescope in Australia when they spotted something odd – a powerful five millisecond burst of radio waves that had gone completely unnoticed at the time. Subsequently known as the Lorimer Burst, it was the prototype for the FRB phenomenon. Since then, we have attuned our instruments to be able to detect these fleeting radio blasts, which can pack in as much power in a millisecond as our Sun will radiate in 80 years, more easily.
As with the detection of any mysterious signal, there is speculation that FRBs could be the product of extraterrestrial activity, and to this day astrophysicists do not know what produces them. However, we’re pretty sure that they are a natural phenomenon. Observations have shown us that the radio waves in FRBs are polarised, which tells us that they emanate from highly magnetic environments. Some are also seen to repeat, allowing astronomers to home in on their galaxy of origin, finding them to just be regular-looking galaxies. The smart money is on them being unexplained emissions from an extreme, compact object such as a magnetar, which is a highly magnetic neutron star.
Hopefully, these examples all help reveal the dilemma facing SETI scientists. Suppose we do detect something unusual in space. It doesn’t have to be a radio signal, it could be some strange behaviour or characteristic of a star, such as the presence of anomalous amounts of heavy elements, as in the case of Przybylski’s Star. Or, the unusual phenomena could be in the form of dips in a star’s light, caused by something puzzling transiting in front of it. Whatever the case, it’s not always immediately clear how we might discern what the cause is. The golden rule in SETI is to first explore every feasible natural explanations, and only when those run out should we start to seriously consider an extraterrestrial explanation. However, when faced with an exotic scientific mystery, it is easy for the media, the public, and even scientists to get carried away.
Consequently, the rumour mill could run rampant with stories of how some strange astrophysical phenomenon is extraterrestrial in origin, and frustration could grow among the public and scientists at large when faced with no obvious means by which to quickly figure out the reality one way or another. How should SETI handle such a case?
The ‘alien megastructure’ star
As it happens, there’s already been a test case that SETI scientists can take lessons from. In 2015, a star catalogued as KIC 8462852 hit the news headlines. Observed by NASA’s Kepler Space Telescope, which hunted for exoplanets by watching for when they transit (pass in front of) their stars, blocking some of the starlight, KIC 8462852 exhibited bizarre dips in light. These dips were initially spotted by citizen scientists on the Planet Hunters website, where members of the public are invited to look at 30-day snapshots of a star’s light curve (i.e. a graph showing how a star’s light varies over time) to see if they can see anything that looks like a planetary transit. The dips in KIC 8462852’s light were so bizarre that they were flagged up for astronomer Tabetha Boyajian, of Louisiana State University, to take a closer look at. She put all the 30-day segments together to create a light curve four years long, and for the first time she saw how truly bizarre the dips are. Whereas a Jupiter-sized planet might block one or two per cent of a star’s light, these dips were blocking much more – at one point, a quarter of the star’s light was obscured. Nor were the dips regular – there appeared to be no pattern, no periodicity, just random transit events. It was as though a swarm of giant objects were swirling around the star, which has since become known as Boyajian’s Star.
Tabetha Boyajian originally suggested that the dips could be caused by a family of giant comets and their long dust tails. However, a conversation between herself and astronomer Jason Wright of Penn State University raised the possibility that the dips could be caused by the transits of something far more exotic: artificial megastructures placed in orbit around the star. This idea was picked up on by journalist Ross Anderson at The Atlantic, and suddenly the ‘alien megastructure star’ became a media sensation. Although there was no evidence that it was aliens, people wanted to believe just like Fox Mulder. The pressure on Boyajian and her colleagues to pander to the media and popular SETI theories rather than conduct a rigorous scientific investigation that would likely rule out the alien explanation must have been immense. It would have been so easy to have become carried away by the media hype, but they didn’t.
Boyajian self-financed funds for new observations of the star via Kickstarter, and those observations came up trumps, showing that the transiting objects are blocking different amounts of light depending on the wavelength. Specifically, shorter (bluer) wavelengths are blocked more than longer (redder) light. If the transiting bodies were solid, they’d block all light equally, whatever the wavelength. Instead, this behaviour of preferentially blocking certain wavelengths is typical of cosmic dust (hence why we use infrared telescopes to see through interstellar dust clouds). The origin of this dust, and whether it is in orbit around Boyajian’s Star or whether it just happens to be somewhere in the 1,400 light-year expanse between us and the star, is still uncertain, but at least we do now know that it isn’t aliens.
So Boyajian’s Star was a false alarm for SETI, but a vital one in the sense that it makes for an excellent test case as to how SETI astronomers should respond when faced with a puzzling astrophysical phenomenon that cannot be solved straight away. It allowed us to see how the media will respond, how scientists will respond, and the steps needed to be taken to get to the bottom of the mystery. Plus, astronomers are beginning to uncover other stars with anomalous transits, indicating that the phenomenon might not be unique to Boyajian’s Star. It’s a brand new astrophysical phenomena for astronomers to study.
Looking for anomalous transits is still a valid method of conducting SETI and searching for technosignatures (i.e. evidence of extraterrestrial technology). The case of Boyajian’s Star, and other stars like it, will help astronomers in the future to better distinguish between natural stellar behaviour and something has the hallmarks of being artificial.
So false alarms in SETI are not to be sniggered at. Quite the contrary, they can be extremely useful in helping to fine tune how we do SETI. We’re learning all the time about what phenomena is out there in the Universe, how to study it better, and how to distinguish it so that we don’t confuse it for a signal from ET, so that the next time we do find something anomalous, maybe it will prove not to be a false alarm after all.